OP ARTS AND SCIENCES. 109 



From these, we calculated — 



Clinodiagonal, a = 1.239 

 Orthodiagonal, 6 = 1. 

 Vertical Axis, c = 3.082 

 Angle of Axes, C = 58° 38' 



We have not been able to study in detail the optical characters of 

 these crystals ; but observations with the polarizing microscope indicate, 

 that, when resting on their prismatic planes, one of the principal 

 optical sections is approximately, but not quite, parallel to the prismatic 

 edges, making an angle with it of about 5°. 



An analysis of the above crystals, made by Mr. Richardson, gave 

 the following results : — 



